D.C. Delegate Eleanor Holmes Norton today said she reviewed her campaign files and found about $20,000 in tainted contributions from people associated with Thompson, who is under federal criminal investigation for a widespread, nationwide scheme to use “straw donors” to make campaign contributions that actually originated with Thompson. The scheme allegedly lasted from 2002 until last year.

Norton said she decided to donate the same campaign amount in her files to D.C. Vote, a nonprofit advocacy organization. She told the Kojo Nnamdi Politics Hour on WAMU 88.5 radio Friday that “only a U.S. attorney” would be able to know that the contributions were being reimbursed.

On the same show, Prince George’s County Executive Rushern Baker said he has checked his campaign finance files, too. He said he received a contribution in 2006 when he was running unsuccessfully for the post he now holds. Baker said he and his campaign staffers are extra careful in accepting donations now, in part because of the Thompson scandal.

Thompson and his attorney have consistently declined comment on the two-year-old federal investigation that had a major development this week.

On Thursday, the clearest indication of the scheme that went on for 10 years came from local businessman Lee A. Calhoun, who pleaded guilty in court to a misdemeanor for his participation in the scheme. Court documents show Calhoun made $160,000 in contributions over 10 years, contributions reimbursed by Thompson, a violation of law.

Calhoun’s attorney Edward MacMahon Jr. told reporters that Thompson was the executive in the case that the court papers only identify as “Executive A.” MacMahon told reporters he expected several other participants in the alleged Thompson scheme to show up in court soon. Just hours after MacMahon spoke, U.S. Attorney Ronald Machen’s office announced that a Pennsylvania businessman will appear in court early next week. The businessman is expected to plead guilty to a misdemeanor for making improper political contributions, just like Calhoun.

Lawyers familiar with the investigations say prosecutors are stepping up their efforts in part to pressure Thompson and his attorney, Brendan V. Sullivan, to meet with prosecutors to explain the scheme or potentially face more serious criminal charges.

Thompson also is at the center of a related federal probe into Mayor Vincent Gray’s 2010 campaign. Court documents show that Thompson helped lead a $650,000 “shadow campaign” that helped finance Gray’s campaign. Gray has declined to comment on that probe and has not been charged with a crime.